The 6" above grade floor hgt. is pretty standard. I would think 3" siding over hang should work, depending on the type of siding used, of course. I understand your location can be very wet at times and you'll have to deal with this as well. You may also need to consider eave rain gutters to help prevent water bounce back onto the siding. I'd tend to avoid wood based siding, like T-1-11, as it does not like water long term.
The garage would have 2' overhang along with gutters and it would be T1-11 to match the existing house. All of the area surrounding the garage would have gravel/roadbase
During a normal year it gets a fair amount of rain and just a few inches of snow at a time
When I spoke with the contractor last night and asked how far the siding would overlap the slab he said a 1/2 inch which after thinking about it didn't seem right to me.
A 1/2" is what I do for any siding I've installed. Vinyl, hardi, aluminum, steel, cedar....
Parge up to the siding after install, to lose the concrete look.